1. Field of the Invention
The present invention is generally related to a marine propeller and, more particularly, to a dual rate torque transmitting device which reduces noise at low torque magnitudes while maintaining the capacity to transmit higher torque magnitudes.
2. Description of the Prior Art
Those skilled in the art of marine propellers are familiar with various devices which have been provided to attach a propeller to a propeller shaft in a way which provides a certain degree of resilience in the torque transmitting connection.
U.S. Pat. No. 4,566,855, which issued to Costabile et al. on Jan. 28, 1986, describes a shock absorbing clutch assembly for a marine propeller. The propeller hub has an axial hole therein having a wavy, non-cylindrical surface consisting of a plurality of alternating peaks and valleys. A closely fitting resilient insert slips into the axial hub hole of the propeller hub and has an outer surface with peaks that extend into the respective valleys of the axial hub hole. The resilient insert has a cylindrical axis hole therein with a plurality of longitudinal keyways disposed in the surface of that hole.
U.S. Pat. No. 4,900,281, which issued to McCormick on Feb. 13, 1990, discloses a marine drive with an improved propeller mounting. The marine drive is intended for use with a boat and includes a longitudinally extending propeller shaft which effectively carries the propeller hub between a pair of fore and aft conical surfaces which mate with similar conical surfaces associated with the hub. These mating surfaces prevent orbiting movement of the propeller. The mating surfaces also center the hub on its axis and provide for high torque retention.
U.S. Pat. No. 5,252,028, which issued to LoBosco et al. on Oct. 12, 1993, describes a marine propeller assembly with shock absorbing hub and easily replaceable propeller housing. A shock absorbing hub for a marine propeller assembly includes an inner spindle telescoped into the splined drive shaft of the engine, an outer sleeve spaced radially outwardly of the spindle, and a molded-in-place core of elastomeric material filling the space between the spindle and the sleeve to transmit torque between the two while cushioning torsional shock.
U.S. Pat. No. 5,322,416, which issued to Karls et al. on Jun. 21, 1994, discloses a torsionally twisting propeller drive sleeve. The drive sleeve is disposed between a propeller shaft and a propeller hub in a marine drive and absorbs shock after the propeller strikes an object by torsionally twisting between a forward end keyed to the propeller hub and a rearward end keyed to the propeller shaft. The drive sleeve is composed of a plastic material providing torsional twisting angular rotation at a first spring rate less than 100 lb. ft. per degree from 0 degrees to 5 degrees rotation, a second higher spring rate beyond 5 degrees rotation, and supporting over 1,000 lb. ft. torque before failure.
U.S. Pat. No. 5,908,284, which issued to Lin on Jun. 1, 1999, describes a marine propeller with a tube shape shock absorbing means. The propeller is made up of a propelling unit having a plurality of blades, a driving unit for driving the propelling unit, and a plurality of deformable transmission units located between the propelling unit and the driving unit such that the transmission units are retained in the retaining slots of the propeller unit and the drive unit.
U.S. Pat. No. 6,383,042, which issued to Neisen on May 7, 2002, describes an axial twist propeller hub. A propeller assembly that includes an interchangeable drive sleeve, a resilient interhub having a bore in which the drive sleeve is inserted, and a propeller including an outer hub in which the drive sleeve and resilient inner hub are inserted, is described. In an exemplary embodiment, the drive sleeve includes a cylindrical shaped body and a plurality of splines extend from an outer diameter surface of the drive sleeve body. A bore extends through the drive sleeve and a plurality of grooves are in an inner diameter surface of the drive sleeve bore.
U.S. Pat. No. 5,244,348, which issued to Karls et al. on Sep. 14, 1993, discloses a propeller drive sleeve. A shock absorbing drive sleeve is provided by a molded plastic member directly mounting the propeller hub to the propeller shaft. The sleeve has a rearward inner diameter portion engaging the propeller shaft in splined relation and a forward inner diameter portion spaced radially outwardly of and disengaged from the propeller shaft. The drive sleeve has a rearward outer diameter portion and a forward outer diameter portion engaging the propeller hub.
U.S. Pat. No. 6,478,543, which issued to Tuchscherer et al. on Nov. 12, 2002, discloses a torque transmitting device for mounting a propeller to a propeller shaft of a marine propulsion system. The device is intended for use in conjunction with a marine propulsion system and provides an adapter that is attached in torque transmitting relation with a propulsor shaft for rotation about a central axis of rotation. The first insert portion is attached in torque transmitting relation with the adapter and a second insert portion is attached in torque transmitting relation with a hub of the propeller hub which can be a marine propeller or an impeller. A third insert portion is connected between the first and second insert portions and is resilient in order to allow the first and second insert portions to rotate relative to each other about the central axis of rotation.
U.S. Pat. No. 6,672,834, which issued to Chen on Jan. 6, 2004, describes a removable propeller assembly incorporating breakaway elements. A propeller assembly is provided for mounting on a rotatable propeller shaft of a marine vehicle. The propeller assembly includes a central adapter mounted on the propeller shaft for rotational movement therewith. A tubular propeller housing is slidable over the central adapter. A bushing assembly translates rotation of the central adapter to the propeller housing. A breakaway element is provided for interconnecting in a central adapter and the bushing assembly. The breakaway allows the central adapter to rotate independently of the propeller housing in response to the predetermined force thereon.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
Attachment devices for connecting a propeller to a propeller shaft of a marine vessel are typically intended to perform several functions. One function relates to the provision of a frangible disconnecting system, such as a fuse, which allows the propeller and propeller shaft to be disconnected from each other in the event that the propeller strikes an object during use. At one time, this function was performed by a shear pin. Now, various types of frangible components can be used for this purpose. A second intended function of many types of torque transfer mechanisms used in marine propeller applications is to permit a preselected degree of relative rotation between the propeller shaft and the propeller hub. A third function that has been provided by certain types of torque transmitting devices used in conjunction with marine propellers is to provide a dual rate torque transmitting connection between the propeller shaft and the propeller hub. During transmission of low magnitudes of torque, rapid accelerations and decelerations of the propeller shaft, relative to the propeller hub, can result in a condition referred to as “propeller rattle”. This phenomenon can be caused by the individual power strokes of numerous cylinders of an engine. It is compounded by various interconnections in a drive train of a marine vessel that can allow intermittent contact and separation between driving and driven elements of the drive system. A marine torque transmitting device used in conjunction with a propeller system must also be capable of transmitting higher magnitudes of torque when the marine vessel is operating at its maximum load and thrust capabilities.
It would therefore be significantly beneficial if a torque transmitting device for a marine propeller could be provided which is sufficiently resilient at low torque magnitudes to reduce the degree of propeller rattle while being sufficiently rigid at higher torque magnitudes to be able to satisfactorily transmit high magnitudes of torque from a propeller shaft to a propeller hub.